1. Field of the Invention
The present invention relates to a brushless motor having a shaft retaining structure.
2. Description of the Related Art
Conventionally, there is a structure for rotatably supporting a motor shaft by using an oil-retaining bearing.
In this structure, a method is employed for attracting a leading end of the shaft in an axial direction by a magnet so that the shaft is not pulled out in the axial direction by the rotation.
In the case of using the magnet, a configuration has been suggested for attaching a magnet holder to an outer periphery of the magnet by a metal plate for attracting and fixing the magnet. An example of such configuration is disclosed in JP-A-2007-236189.
The magnet holder disclosed in JP-A-2007-236189 is fixed in the following manner.
In the configuration disclosed in JP-A-2007-236189, a bearing for rotatably supporting the shaft is fixed to a bearing holding part. A recessed shape or hole is formed at a bottom portion of the bearing holding part. The magnet holder is fixed by being press-fitted into the recessed shape or hole formed at the bottom portion of the hearing holding part.
However, in the process of forming the bottom portion of the bearing holding part in the recessed shape and press-fitting the magnet holder into the recessed shape, a small part is inserting into the bottom portion of the healing holding part and additionally applying a pressure for press-fitting the magnet holder therein. Here, during the press-fitting, the small part is subjected to pressure. Therefore, a workability in assembling the motor is poor.
Furthermore, it is essential to install a magnet that is magnetized to the magnet holder made of a magnetic material. Accordingly, the magnet may be stuck to a collar portion of the magnet holder by a magnetic force. As a result, the process may become more complicated.
On the other hand, in the case where a hole is drilled at the bottom portion of the bearing holding part and the magnet holder is press-fitted into the hole, not only the workability is poor, but also there is a possibility that a slight gap occurs between the bottom portion of the bearing holding part and the magnet holder. As a result, there is a possibility that oil in the oil-retaining bearing will leak from the gap. As a method of filling the gap, JP-A-2007-037365 discloses a technique for applying oil-repellent agent to the magnet holder and thus repelling the oil.
However, the oil-repellent agent may solve the problem of oil leakage but may not solve the man-hour problem described above.